This invention relates to a hydraulic control system and more particularly to hydraulic clutch actuators for use in motor vehicles.
Motor vehicle clutches originally were actuated by mechanical systems and, later, by hydraulic actuators including a master cylinder, a slave cylinder, and a conduit interconnecting the master and slave cylinder so that depression of the clutch pedal operates to discharge fluid from the master cylinder for delivery to the slave cylinder to move the output member of the slave cylinder outwardly to release the clutch.
Later, as shown for example in U.S. Pat. No. 4,599,860 assigned to the assignee of the present invention, the hydraulic clutch actuators were provided in a prefilled form to avoid filling of the apparatus on the vehicle assembly line with the prefilled apparatus including an expansible seal in the reservoir of the apparatus such that in the filled apparatus the seal is in contact with the fluid to prevent the ingestion of air into the apparatus but to permit the expansion and contraction of the fluid occurring in response to operation of the system, leakage in the system, and wear in the associated clutch assembly. Prefilled systems including an expansible seal in the reservoir have proven to be enormously successful and have virtually replaced hydraulic clutch actuators of the non prefilled type.